Many devices, such as fans, use a motor to achieve the purpose of transmission. Therefore, the quality of a motor plays a very important role in the performance of a motor-driven device. A motor failing to work stably would no doubt adversely affect the whole operation of the device. Among others, the bearing is one of the most important factors that have influence on the quality of a motor.
Conventionally, a fan is formed by injection molding a plastic material. In the manufacturing process of the fan, a central tube of the fan is integrally injection molded along with a bearing, so that the bearing is fixedly held in the central tube to allow stable operation of a motor of the fan. While the bearing can be held in the central tube when the fan is injection molded with a plastic material, the bearing is not held in the central tube in a desired condition good for stable motor operation. This is because the plastic material is subject to thermal expansion and cold contraction, and it is therefore difficult to control correct fitting tightness and required range of fitting allowance between the bearing and the central tube in the process of manufacturing the bearing and the central tube. That is, it is uneasy to achieve proper fit between the bearing and the central tube. For example, in the event the bearing is too tightly fitted in the central tube, it would result in the formation of shrinkage holes on the bearing. On the other hand, in the event the bearing is too loosely fitted in the central tube, it would not be able to effectively hold the bearing in place in the central tube and result in low fitting accuracy and poor fitting allowance. Thus, the conventional way of forming a fan through plastic injection-molding fails to effectively hold the bearing in place in the central tube, and it is uneasy to control the fitting accuracy between the bearing and the central tube in the manufacturing process. These drawbacks in turn cause unstable operation of the fan motor.
In another type of fan structure, the central tube is made of a metal material and is integrally formed with the frame of the fan through insert molding. The metal central tube is processed by machining and therefore has relatively high process precision, which enables proper fitting of the bearing in the metal central tube to overcome the drawbacks in the plastic injection-molded fan. However, the metal central tube involves relatively complicated structure and machining procedures. For example, the metal central tube must be additionally machined to provide a shoulder portion therein for supporting the bearing in the central tube. Therefore, the use of the metal central tube inevitably increases the overall manufacturing cost of the fan.
In brief, the prior art fan bearing retaining structures have the following disadvantages: (1) having low fitting accuracy and poor fitting allowance between the bearing and the plastic central tube; (2) failing to effectively hold the bearing in place to thereby cause vibration of motor; (3) requiring increased cost for manufacturing a metal central tube for stably holding a bearing therein; and (4) involving complicated manufacturing processes and accordingly increased labor and time.
It is therefore tried by the inventor to develop an improved fan bearing retaining structure to overcome the disadvantages in the prior art.